LTC3550EDHC#PBF Linear Technology, LTC3550EDHC#PBF Datasheet - Page 21

• Manufacturer Part Number: LTC3550EDHC#PBF
• Description: IC CHARGER BATT DUAL 16-DFN
• Manufacturer: Linear Technology

Specifications of LTC3550EDHC#PBF

• Function: Charge Management
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 4.3 V ~ 8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-WFDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIO S I FOR ATIO
1. The power traces, consisting of the GND trace, the SW
2. Does the V
3. Does the (+) plate of C
4. Keep the switching node, SW, away from the sensitive
5. Keep the (–) plates of C
6. Solder the exposed pad on the backside of the package
trace and the V
and wide.
tors? The resistive divider R1/R2 must be connected
between the (+) plate of C
possible? This capacitor provides the AC current to the
internal power MOSFETs.
V
possible.
to PC board ground for optimum thermal performance.
The thermal resistance of the package can be further
enhanced by increasing the area of the copper used for
PC board ground.
FB
node.
FB
pin connect directly to the feedback resis-
CC
U
VIA TO
VIA TO
trace should be kept short, direct
V
GND
OUT
IN
U
connect to V
OUT
IN
and ground.
and C
R2
R1
C
F
W
V
CC
Figure 7. DC-DC Converter Suggested Layout
OUT
CC
as closely as
as close as
C
IN
U
V
FB
GND
Design Example
As a design example, assume the LTC3550 is used in
a single lithium-ion battery-powered cellular phone
application. The battery is charged by either plugging
a wall adapter cable into the phone or putting the phone in
a USB cradle. The optimum charge current for this parti-
cular lithium-ion battery is determined to be 800mA. The
buck regulator output voltage needs to be 1.8V.
Starting with the charger, choosing R
programs the charger for 806mA. Choosing R
be 2.1k programs the charger for 475mA when charging
from the USB cradle, ensuring that the charger never
exceeds the 500mA maximum current supplied by the
USB port. A good rule of thumb for I
tenth the full charge current, so R
1.24k (I
Moving on to the step-down converter, V
ered from the battery which can range from a maximum
of 4.2V down to about 2.7V. The load current requirement
C
TERMINATE
OUT
V
OUT
= 80mA).
SW
VIA TO V
L1
CC
RUN
3550 F07
ITERM
TERMINATE
LTC3550
IDC
CC
is picked to be
to be 1.24k
will be pow-
21
IUSB
is one-
3550fa
to